Conventional methods of extracting and refining copper are described by A. Butts in "Copper the Metal its Alloys and Compounds" Reinhold Publishing Corp., New York, 1954. The most common method is pyrometallurgy through flotation of crushed ore, then smelting in an oxidising atmosphere to blister and anode copper, and finally electrorefining of anodic to cathodic copper, via acidic cupric sulphate solutions. This method has the disadvantages of pollution by sulphur dioxide, high capital and operating costs and losses of valuable materials in fumes and slags. Another method is that of hydrometallurgy, i.e. leaching copper oxides or sulphides with sulphuric acid, sometimes in the presence of ferric sulphate, to give cupric sulphate solutions. Copper itself can be dissolved in hot sulphuric acid under oxidising conditions to give cupric sulphate solutions. In these methods the cupric sulphate solutions are then stripped of their copper by electrowinning or cementation. More recent procedures include treating the ore with an oxidising or reducing roast, the TORCO segregation process, bacterial leaching, and leaching with ferric chloride or ammoniacal solutions. All these processes, require a final step of electrorefining or electrowinning via aqueous acidified cupric sulphate solutions, if one is to produce copper of sufficient purity for many commercial processes. The electrorefining step is a slow process, typical tankhouse cycles being 11-14 days. A number of tankhouse staff are needed, handling of anodes, treatment of slimes, attention to short circuits and cathode quality, all create problems. The electrowinning process is also slow and consumes considerable quantities of power, but costs associated with anode handling are reduced, compared to electrorefining.